/*
 * Copyright (C) 2016 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.graph;

import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Set;
import javax.annotation.Nullable;

/**
 * An interface for representing and manipulating an origin node's adjacent nodes and edge values in
 * a {@link Graph}.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 * @param <V> Value parameter type
 */
interface GraphConnections<N, V> {

    Set<N> adjacentNodes();

    Set<N> predecessors();

    Set<N> successors();

    /**
     * Returns the value associated with the edge connecting the origin node to {@code node}, or
     * null if there is no such edge.
     */
    @Nullable
    V value(Object node);

    /** Remove {@code node} from the set of predecessors. */
    void removePredecessor(Object node);

    /**
     * Remove {@code node} from the set of successors. Returns the value previously associated with
     * the edge connecting the two nodes.
     */
    @CanIgnoreReturnValue
    V removeSuccessor(Object node);

    /**
     * Add {@code node} as a predecessor to the origin node. In the case of an undirected graph, it
     * also becomes a successor. Associates {@code value} with the edge connecting the two nodes.
     */
    void addPredecessor(N node, V value);

    /**
     * Add {@code node} as a successor to the origin node. In the case of an undirected graph, it
     * also becomes a predecessor. Associates {@code value} with the edge connecting the two nodes.
     * Returns the value previously associated with the edge connecting the two nodes.
     */
    @CanIgnoreReturnValue
    V addSuccessor(N node, V value);
}
